Thanks.
It would be nice if I could take a few simple measurements. Let's say seat height, leg length, clear position, torso angle and then come up with a simple formula.
It won't be that simple as I'm sure that using shorter cranks will then enable a change in all of the other variables.
Aarrgh!
I've got two years to figure it out.

There is definitely a large swath of fans who believe that these guys are thoroughly tweaked, optimized, and know every trick in the book to go fast on TT bikes. I used to to think that. I don't any more.

I don't believe they all are by a long shot, but some. And they have the financial resources as well. Do you believe Sky hasn't looked at crank length? They certainly aren't beholden to tradition.

The pros who care about TTing are going >32mph (51.5km) on the flat. I just watched the 2009 Worlds where Cancellara averaged slightly more than that on a hilly technical course. Don't you think the fact that their events are short and they are riding at ~FTP could skew things a little? Cycling pros also need to consider what works on the road bike. A triathlete rides at a lower fraction of FTP, and the run is most important so they are never at the limit of what they could do for the duration. They are also nearly always fit in a more "comfortable" position.

KingMidas wrote:

I’m currently on 165mm.
Want to try 150-155mm but I don’t know where to find them. Any ideas?

https://cobbb2b.com/...ariant=6067235815467

Bike fitter for about 12 years, about 3000 fits. I'm decent at it. I've always tried to learn from those better than me and over the years, there have been a few tricky questions that I was having a hard time answering until I started experimenting with shortening cranks.

1. Seat too high! - Two angles are the primary drivers of the short crank movement. Knee flexion at the top of the stroke and, probably to a lesser degree, thigh torso clearance at the same point. Raising the seat opens both of these angles, so pedaling can feel better. It is not until later that we come to find that seat height may be causing us other problems.

2. Inability to rotate at the hips, or staying rotated rearward on the saddle, aka - posterior pelvic tilt instead of anterior. Also aka - "riding it like a road bike". Posterior rotation relieves thigh - torso pinching, and I have seen this tendency minimized or in some cases instantly and completely disappear once crank length was addressed. It doesn't really address the knee flexion issue directly, but it can move the overly flexed knee to an earlier portion of the stroke, which can be of some benefit, so perhaps a tertiary benefit to excessive knee flexion? Knee flexion is an issue because the knee can't be extended with close to max power from an overly flexed position. So if we can reduce the flexion or move the overly flexed knee back and away from the powerful portion of the stroke, we have made it better. Unfortunately, anterior pelvic tilt is not the fastest way for most of us to ride.

3. Excessive forward movement on the saddle You know the rider who no matter how far forward the saddle is moved, continually gravitates to the very tip of it, in some cases approaching an actual 90° of seat tube angle. IF everything else stays fixed, sliding forward will open the hip angle, at least the FIST defined "major" hip angle as I have come to refer to it, but other angles can become cramped. But IF we come forward AND raise the saddle (which we should), then it is more obvious how both thigh torso and knee flexion can benefit.

Anyway, just some quick observations that have been solidifying in my brain lately. I'm sure I was unclear about something and will be called out for my ignorance. I am not trying to dictate to the forum, as much as throw out some ideas and get some feedback on your experience as a rider or a bike fitter.

Finally, this is a rough range of crank lengths that riders have been selecting as a loose function of seat height.

<60cm seat height :: Crank 145mm or less. Really as short as you can find, maybe go custom. I’ve fit down to 135mm with custom cut BMX cranks.
60-65cm :: Crank length 140-145mm
65-70cm :: 145-150mm
70-75cm :: 150-155mm
75-80cm :: 155-160mm
80-85cm :: 160-165mm
>85cm :: 165-170mm, maybe 172.5 Keep in mind that of the tallest, strongest professional athletes I have fit literally ZERO of them have preferred anything over 165mm. These are 6’3” and taller athletes pushing wattage over 375 watts at threshold and upper 200s to 300 for IM races.

I’m not understanding

So if I have say 175 cranks and I change to 150s then does the distance from my saddle to the bottom of the b peddle stroke decrease 25 and would have to lower or raise seat 25 to have the same distance if I am happy with the current distance?

No. To replicate the same fit on shorter cranks, you raise the saddle when going to a shorter crank.

First of all, forgive me for getting in and forgive my English
I use a translator
I'm just going to comment that I went through several cranks in tt, 175, 172,5, 170, 165, 150 and returned to 170

You can say the comments that you like, since I'm not a pro or anything like that.
I am an amateur who spends many hours training.
I could say that when I reached 165 my ftp was kept but with strange sensations.
I even went to 150, and I could not keep the test for 20 minutes in indoor, or in the street 1 hour, the same power.
I wanted to be able to, and keep a new cranks that I had recently bought in 150
but I could not adapt, or talk if I went out on the road with fellow riders, on the slopes, abrupt changes of pace, it was not the same.
now I'm in 170, with a seat cobb 55
height 175 cm
layers that someone could tell me I needed more time, the time I gave to the 150 were 2 months

sorry my english

1 things for sure. I or (you) can't climb for shit with short cranks!

While I may look prettier taking pics of me in fit studio in real world my 155s were dogshit.

Stick to as long of crank as reasonably possible.

Imo this 'short crank theory' is a way to generate revenue. Etc

*Speaking honestly here*

No. To replicate the same fit on shorter cranks, you raise the saddle when going to a shorter crank.

1 things for sure. I or (you) can't climb for shit with short cranks! *

In other words, you want to start with the same leg extension, which means moving the saddle up the same amount that the crank length was shortened.

Very true, except there are like a dozen bike fitters out of a many thousands that actually get it. Seriously, how many fitters do you know and recommend? I struggle to compile a list of a few dozen. And you're one of them. I think education is key for all competent fitters to have more business, and it seems like this particular issue really needs to be beaten like a dead horse.